Watching the TV last night - in the UK- saw a prog about rebuilds using injection instead of the original carb.

They claimed much better fuel economy.

So, the question is, two identical engines in good tune - how much more economical would the injection motor be ???

 

Electronic injection with closed-loop O2 feedback and timing control would be more economical due to the ability to manage leaner cruise A/F ratios without tip-in difficulties and the ability to compensate for density altitude changes.

 

What he said...

 

To give you an idea... my 350 '64 roadster with a well-tuned carb and a very well tuned ignition curve gets about 14 mpg. My TPI-injected 350 '85 Coupe gets 26.... (almost 100% better fuel economy).

 

Am slightly worried about that comparison because of aerodynamics, weight and gearing...........and if so - someone must be making a fortune out of a retro injection system - cos with todays gas prices all carbs would be in the trash bin.............

 

 

Carb - good
TBI - Better
Batch FI - Betterer
Seq FI - Bestest

 

No doubt you CAN do better with EFI...but you would be amazed at how well carbs can do on serious motors with big cams etc.

A couple of years ago a bunch of us drove from TX to Bowling Green. One C-3 had a 454, aluminum heads, healthy roller cam, Tremec OD and 3.08's. He got right around 21mpg on every tank with his laptop tuned Holley EFI system. Plus he did have A/C running!

The other was another C-3, but with a 540" bigblock, aluminum heads, healthier roller cam, a single plane intake along with an out of the box 1000cfm HP Holley carb. He also has a Tremec and 3.08's. He regularly got just under 19 mpg...but he didn't have A/C.

On another trip, the two cars drove to the track together after filling up, made several runs (the 540 made one more!) and drove back and filled up together. They both avg'd 15 mpg for the trip!

Now of course I was a little behind at about 11-12 mpg with my "slightly" healthier cam in my 540 and no O/D and a Dominator carb.

Another buddy only managed 15 mpg with his 327 in his '65 with 3.36's.

Anyway, I think you have to really want the EFI to make it pay for itself. For sure you can get great driveability with a radical motor.The first C-3 above does just that..it is by far the smoothest of the bunch and still runs deep into the 12's in pure street trim. I think that's the best advantage..but a simple carb can do OK.


JIM

 

Will EFI pay for it's self?? NO! The amount of miles you would have to drive to save enough money to pay for the EFI would be stagering. But that is only a small reason why I am putting EFI on my wifes 74 vert. The top reasons are:
* starts first time, every time
* no choke to mess with (see above)
* much better throttle response and part throttle drivability
* The wife trusts it better
* Holley carbs make excellant door stops

EFI is awsome and I don't ever want to have to deal with another carb if I can help it. But I wouldn't recomend installing and especially tunning one unless you have extensive expesience tunning carbs. The principals are the same as tunning a carb. You just stay cleaner.

 

Actually closed loop isn't for economy its for emissions. It tries for around the 14:1 ratio while a set fuel curve can go way lean when it don't need to be stochy or even rich.
FI can save fuel in a few other tiny areas. When you take your foot off the gas the injectors can be shut off completely, or nearly so. Little fuel curve affects like that.

Also almost all fuel injection today controls the ignition. This is another HUGE plus that kind of is forgotten when EFI VS carb is being considered.

How much would a conversion save? who knows it does save though.
Add in OD and highway rear ends to save gas though. Thats what makes fuel economy not 4 or 6 cylinder engines.
427Hotrod post kind of proves that. All modern cars have more gears in either manual or auto and all rear ends are generaly anemic compared to this era. All trucks using identical engines get the same milage as this era since they are still using the same final drive as we do.

 

Ok, now I got it in writing! You've called my cam "wimpy" for years and now you admit it's "healthy"!!! What made you change your mind?

 

well i get 18-22 mpg with a tuned port injected 60 over 350 with a .510 roller cam flat top pistons,sportsman 2 heads with a 700r4 and 3.70 gears so aerodynamics has nothing to do with it.

"Am slightly worried about that comparison because of aerodynamics"

 

You serious ???????????

If aerodynamics does not change mpg lets all drive 1966 Galaxies or 1958 Buicks

 

I have put alot of thought into getting better gas mileage lately with fuel injection and/or an overdrive transmission (auto or manual). I have finally come to the conclusion that the most fuel mileage will come from a manual overdrive transmission. I currently have a TH400 and 3.55 rear gear and mileage is dismal at best. My carb is finely tuned, as is my ignition system. The cost of an aftermarket or GM fuel injection system, in my opinion, is not worth the money or effort compared to the gains I believe possible with an OD tranny.....not to mention the fun factor for me switching to a manual!

 

or those Scion pieces of crap...

 

i was comparing lars's 2 cars not todays cars and his 85 vette to my 73 we get close to the same mileage ,same injection

 

Awww.....jeez....now you caught me......busted!

Let's see...how do I skate out of this one......

I guess it's all in the context of who else's motors are in the vicinity at the time.

Well.....it IS a healthy cam for a nice street toy and it DOES run 12's.....and it does get 21 MPG..so it can't be ALL bad.


BUT...what it REALLY needs is.......a HEALTHIER...less wimpy (in the grand scheme of things) cam!!


11's would be even better with A/C!!

BTW...got the 1.8 rockers.....only .774 lift on intakes!
But I still have .170 P/V clearance...I must need more cam!

I mean in that context....Nick has to step up some!!


JIM

 

For most fuel economy upgrades, OD included, you'll probably have to drive >30k miles. Personally, I wouldn't switch unless you were doing it for other reasons, ie drivability, reliability, etc. I calculated that I'd have to drive 70k miles with overdrive to regain the cost of the swap, but I did it to improve drivability and because the old TH400 was leaking. Even new hybrids need to drive quite a while before they offset the large initial cost of hybridization.

 

FI should be worth 30% min.

 

FWIW I gained about 1mpg when I switched. went from 12/21 to 14/22 city/highway. I switched from the computer controlled carb to a sequential fuel injection system.